What's the difference between i.e. and e.g.?
in physics, any discrete value from a set of values of total energy for a subatomic particle confined by a force to a limited space or for a system of such particles, such as an atom or a nucleus. A particular hydrogen atom, for example, may exist in any of several configurations, each having a different energy. These energy states, in their essentials, remain fixed and are referred to as stationary states.